The present patent application claims the benefit of earlier Japanese Patent Application No. 2000-195165 filed Jun. 28, 2000, the disclosure of which is herein incorporated entirely by reference.
1. Field of the Invention
The present invention relates to a plasma processing apparatus for producing plasma under application of a radio frequency and for carrying out etching or CVD processes.
2. Description of the Related Art
A parallel plate type plasma etching apparatus is generally used in semiconductor manufacturing processes. In the conventional plasma etching apparatus, a radio frequency of about 13.56 MHz is applied to the cathode electrode to excite plasma. However, in order to keep up with increasingly strict design rules, and in order to respond to a demand for improvements in productivity, techniques of applying a higher range of radio frequency, e.g., the frequency band of VHF to UHF have been studied. The proposal of raising the radio frequency applied to the electrode also responds to a demand for an increase in wafer size, in which more intricate patterns are to be formed.
However, as the frequency applied to the electrode becomes higher, the loss of RF power also increases. If the loss of RF power increases, the electron density of plasma produced between the parallel plate electrodes decreases, lowering the etching rate. Consequently, a wafer cannot be precisely etched into a designed shape and pattern.
FIG. 1 illustrates a conventional plasma processing apparatus. The conventional apparatus comprises an RF electrode 4, to which an RF is applied, and a metallic DC plate 2, to which a direct-current voltage is applied, a ceramic or resin insulator 3a, and an opposite electrode 5 facing the RF electrode. The conventional RF electrode 4 is made relatively thick because the RF electrode itself has a wafer support function. The RF electrode 4, the DC plate 2, and the insulator 3a and 3b constitute a wafer hold structure.
As illustrated in FIG. 2, pusher pins 12 extend penetrating the RF electrode 4, the DC plate 2 and the insulator 3b. The pusher pins 12 are used to place a wafer 1 onto the RF electrode 4. When the wafer 1 is transported into the housing 7, the pusher pins 12 elevate and project above the RF electrode 4 to receive the wafer 1. Then, the pusher pins 12 are lowered to place the wafer 1 onto the insulator 3b. 
The wafer 1 is securely held on the RF plate 4 by an electrostatic chuck consisting of the insulator 3b and the DC plate 2. A positive voltage of 1000V to 3000V is applied to the DC plate 2 from the DC power source 11. In this situation, if a radio frequency is applied to the RF electrode 4 to produce plasma, the wafer 1 is charged up negatively and attracted to the DC plate 2 that is at a positive voltage. A low pass filter 13 prevents the RF power, which is applied to the RF electrode 4 and transferred to the DC plate 2 via the parasitic capacity between the RF electrode 4 and the DC plate 2, from flowing into the DC power source 11.
In the conventional plasma processing apparatus shown in FIGS. 1 and 2, as the radio frequency applied to the electrode is raised, loss due to the inductance and the parasitic capacity of the hot lines becomes large. This means that the loss of the RF power also increases.
The most significant example of loss due to the raised radio frequency is the growth in parasitic capacity relative to the capacity of produced plasma. To be more precise, as the radio frequency becomes higher, the plasma density increases, as illustrated in FIG. 4B. On the contrary, the plasma capacity itself abruptly decreases as the frequency increases, as shown in FIG. 4A. For this reason, the parasitic capacity existing between the RF supply line through which the radio frequency propagates and the grounded portion of the housing 7 becomes almost equal to the plasma capacity (that is, the parasitic capacity increases relatively). This means that, apart from that used for producing and maintaining plasma, the RF power supplied to the apparatus is wasted.
Another problem in the conventional plasma processing apparatus is the parasitic capacity existing between the RF mount electrode 4 and the pusher pins 12. As is illustrated in FIG. 2, the conventional RF mount electrode 4 is made relatively thick because it is designed to function as both an electrode and a wafer mount stage. The pusher pins 12 always face the metallic electrode 4 even after it retreats inside the RF mount electrode 4, producing parasitic capacity between the pins and electrode 4. This parasitic capacity causes a loss in RF power.
Such a loss becomes particularly marked if the applied radio frequency is 60 MHz or higher. Accordingly, the reduction of parasitic capacity is one of the most serious problems to be solved. In order to reduce the parasitic capacity, the entire apparatus, including the heat sink structure and pusher pin arrangement, must be configured optimally.
Still another problem in the conventional apparatus is the loss of RF power from the electrostatic chuck. As has been mentioned above, the radio frequency applied to the RF mount electrode flows into the low pass filter 13 via the DC transmission line, and is consumed in this filter. This occurs because the low pass filter 13 consists of lumped-constant reactance elements, and has large parasitic capacity. As the radio frequency becomes higher, loss or the consumption in the low pass filter 13 increases. The radio frequency flowing into the low pass filter 13 may cause the break down or burning of the low pass filter, and may damage the DC power source 11.
On the other hand, it is desirable to reduce the volume of the housing 7 as much as possible in order to produce plasma efficiently, while reducing the quantities of precursor gases introduced into the apparatus. To reduce the volume of the apparatus, it has been proposed to use the heat sink (or insulator) that supports the RF electrode and a wafer as a vacuum chuck itself. However, the interface between the metallic housing and the ceramic sink is located at the boundary between the vacuum and the atmosphere. Consequently, the heat sink becomes brittle and is likely to break.
Therefore, to overcome the problems in the prior art technique, a plasma processing apparatus that can reduce a loss of RF power even if a radio frequency of 60 MHz or higher is applied to the electrode is provided in one aspect of the invention. In this apparatus, the plasma capacity is increased relative to the parasitic capacity by reducing the parasitic capacity of the apparatus as a whole. This plasma processing apparatus comprises a grounded housing, a thin RF plate electrode placed in the housing, an opposite electrode facing the RF plate electrode, and an RF power source for applying a radio frequency to either the RF plate electrode or the opposite electrode. By applying a radio frequency to either electrode, plasma is produced between the RF plate electrode and the opposite electrode. If the radio frequency applied to the electrode is f (MHz), the parasitic capacity C (pF) between the grounded portion of the housing and a conductive portion through which the radio frequency propagates is less than 1210*fxe2x88x920.9.
In another aspect of the invention, a plasma processing apparatus comprises a grounded housing, an RF plate electrode placed in the housing, an opposite electrode facing the RF plate electrode, and first and second radio-frequency power sources. The first and second radio-frequency power sources apply different values of radio frequencies to either the RF plate electrode or the opposite electrode. One of the radio frequencies applied to the electrode is 60 MHz or higher. If this radio frequency is f (MHz), the parasitic capacity C (pF) between the grounded portion of the housing and a conductive portion (or hot lines) is also less than 1210*fxe2x88x920.9.
In still another aspect of the invention, a plasma processing apparatus having an improved pusher pin structure for reducing the parasitic capacity is provided. In this apparatus, the parasitic capacity between the RF plate electrode, to which a radio frequency is applied, and pusher pins is substantially eliminated, thereby greatly reducing the loss of RF power. This plasma processing apparatus comprises a grounded housing, a wafer mount electrode having at least two holes passing through it, an opposite electrode facing the wafer mount electrode, an RF power source, and pusher pins inserted in the holes. The wafer mount electrode includes an RF plate electrode having a thickness of 6 mm or less and an insulator for supporting the RF plate electrode. The pusher pins are movable between a first position, at which the pusher pins project out of the wafer mount electrode to receive a wafer, and a second position, at which the pusher pins retreat below the RF plate electrode during the generation of plasma.
In yet another aspect of the invention, a plasma processing apparatus that can reduce the loss of RF power, eliminate adverse influence to the DC power source, and produce plasma at a high density, is provided. This plasma processing apparatus comprises a wafer mount electrode, an opposite electrode facing the wafer mount electrode, a DC power source, and RF power source, and a radio-frequency trap positioned between the wafer mount electrode and the DC power source. The DC power source supplies a direct-current voltage to hold a wafer on the wafer mount electrode in an electrostatic manner. The RF power source applies a radio frequency to either the wafer mount electrode or the opposite electrode to generate plasma between the two electrodes. The radio-frequency trap has an electrical length of (2n+1)/4 wavelength of the applied radio frequency, where n is 0 or a natural number.